1. Field of the Invention
The present invention relates to a method for manufacturing a homeotropic alignment liquid crystal film. Moreover, the present invention relates to a homeotropic alignment liquid crystalline composition and a method for manufacturing a homeotropic alignment liquid crystal film using the homeotropic alignment liquid crystalline composition. Furthermore, the present invention relates to a homeotropic alignment liquid crystal film and an optical film obtained by the above-mentioned manufacturing method. Moreover, the present invention relates to a visual display, such as a liquid crystal display, an organic EL display, a PDP (plasma display panel), etc., using the above-mentioned optical film. A homeotropic alignment liquid crystal film may be used as a retardation film, a viewing angle compensating film, an optical compensating film, and an elliptical polarization film independently or in combination with other optical films.
2. Description of the Related Art
Homeotropic alignment of a liquid crystal compound is obtained when the major axis of a liquid crystal phase molecule in a thin film substrate is generally substantially vertical to the film plane. Since substances that spontaneously provide homeotropic alignment are hardly known, a vertical alignment agent is generally used in order to obtain such alignment. For example, nematic liquid crystal compound is an example of a liquid crystal compound that can provide homeotropic alignment by using a vertical alignment agent. Such an outline in connection with an alignment technology of liquid crystal compound is discussed in Chemical Review 44 (Surface Reforming, edited by Chemical Society of Japan, pages 156–163).
Various kinds of organic or inorganic alignment agents are known as vertical alignments agents to homeotropically align the above-mentioned liquid crystal compounds. Many of the alignment agents commonly used are designed to be effective when used on glass substrates.
Examples of organic alignment agent include: lecitin, silanes type surface active agents, n-octadecyl triethoxy silane, titanates type surface active agent, pyridinium salts type high molecular surface active agent, hexadecyl trimethyl ammoniumhalide, or chromium complex. Organic alignment agents are dissolved in suitable volatile solvents in which active ingredient is in a very small amount (typically less than 1%), and coated by a spin coating or other well known coating methods on a substrate. Subsequently, the volatile solvent is evaporated to give a thin film of organic alignment agent on the glass substrate. These organic alignment agents are compounds characterized by polar end groups drawn onto polar glass surface and linear alkyl chains with non-polarity vertically arranged to glass surface. Thus, the agents have the liquid crystal compounds form homeotropic alignment on such a glass surface.
Inorganic homeotropic alignment agents include compounds that may be coated by vapor deposition, such as SiOx or In2O3/SnO2, at a vertical angle onto a glass substrate. In addition, polyimide films with alkyl side chain are also used as homeotropic alignment films for a liquid crystal display.
However, all of the above-mentioned alignment agents commonly used provides homeotropic alignment of liquid crystal compound only on glass substrate, and do not act effectively in alignment on substrates consisting of polymer substances such as plastic films and sheets plastics. A surface of a substrate consisting of a polymer substance may be presumed to have poor affinity to polar end groups of commonly used alignment agents described above, and as a result generally do not show homeotropic alignment at all, or shows very poor alignment. Moreover, high temperature treatment is required for formation of polyimide film with alkyl side chain. However, transparent plastic films for optical use that have durability to temperature conditions in which polyimide alignment films are baked are hardly known.